The present invention relates to a detergent dispenser which comprises a powder detergent and a pouch or bag containing the powder detergent, wherein the pouch is made of a cold water soluble polyvinyl alcohol derivative. The pouch of the present invention is resistant to acid and to alkali and can retain its solubility over a long period of time. The pouch or bag containing the powder detergent is capable of dissolving when it is placed into water.
Polyvinyl alcohol (hereinafter referred to as "PVA") is a water-soluble polymer which is widely used for water-soluble films and in other fields. PVA which has a degree of saponification ranging from 80 to 95 mol % exhibits a rapid water solubility. PVA which has a degree of saponification of at least 98 mol % is called "completely saponified PVA" and is dissolved in water when it is allowed to stand in the water for a long period of time or if it is placed into hot water. However, completely saponified PVA does not promptly dissolve in cold water.
PVA having a degree of saponification ranging from 80 to 95 mol % is stable in a neutral pH region, however, when it contacts an alkaline substance, saponification of the remaining ester groups increases and the degree of saponification deviates from the above-mentioned range and exceeds this range. Accordingly, prompt solubility in cold water is lost.
The reason why completely saponified PVA is not immediately soluble in water is because the polymer is crystalline. More specifically, it is believed that because the hydroxyl groups of PVA form very strong hydrogen bonds intermolecularly, then crystallization results and the intrusion of water molecules is inhibited. This is reported by Sakurada et al. in Kobunshi Kagaku, Vol. 12, No. 128, pages 510-513 (1955).
Furthermore, in the report of Sakurada et al. in Kobunshi Kagaku, Vol. 12, No. 128, pages 517-521 (1955), it is taught that the degree of crystallization of completely saponified PVA is increased by heating, and that the increase in the degree of crystallization participates greatly in reducing the solubility.
Moreover, in the report of Sakurada et al., Kobunshi Kagaku, Vol. 12, No. 128, pages 510-513 (1955), it is shown that the crystal region does not participate in the swelling of PVA.
Accordingly, if it is supposed that "dissolution" corresponds to infinite swelling in which molecules of PVA are disjointed, it is necessary to prepare substantially complete amorphous PVA in order to obtain cold water-soluble, completely saponified PVA. In other words, it is necessary that crystallization should be prevented by putting the regularity into disorder.
Given this background, a process for synthesizing atactic PVA while reducing the crystallinity is proposed in Kobunshi Ronbunshu by Imai et al., Vol. 35, No. 12, pages 811-813 (1978) and Japanese Patent Publication No. 36-3999. However, since preparation is possible only under strictly limited conditions in this process, industrial production is considerably difficult.
In order to obtain a PVA having improved properties, an alkoxybutyralization product of PVA is proposed in Japanese Patent Publication No. 38-20720. According to this technique, however, since the chain of the aldehyde used for acetalization is long, and if the degree of acetalization is controlled within a range capable of imparting water solubility, then the acetalization has to be maintained at a low level. Therefore, the disorder of the structural regularity cannot be maintained for a long time, which results in an increase in the degree of crystallization and a decrease in the degree of water solubility.
A technique using acetalized PVA as the water-soluble PVA derivative is disclosed in an example of Japanese Patent Publication No. 39-16910. According to this technique, a non-ionic surface active agent is added to acetoacetalized PVA. Since the average degree of polymerization of acetoacetalized PVA is 550, if commercially available PVA (composed mainly of a syndiotactic polymer) is used, an increase in the degree of crystallization over time cannot be avoided, as in the above-mentioned conventional technique, and therefore, the water solubility is lost. According to the report of Sakurada et al., Kobunshi Kagaku, Vol. 12, No. 128, pages 506-510 (1955) concerning the relationship between the degree of crystallization and the average degree of polymerization of PVA, it is taught that the increase in the average degree of polymerization results in an increase in the degree of crystallization. This means that the increase in the average degree of polymerization results in a reduction in the water solubility.
Furthermore, a technique using partially aldolacetalized PVA is disclosed in Japanese Patent Publication No. 42-2-845. This partially aldolacetalized PVA is prepared by an acetalization reaction between an aldol and PVA. Since both hydroxyl and aldehyde groups are present in a molecule of aldol, a reaction of the molecules of aldol with each other takes place and control of the reaction is difficult. This means that it is very difficult to prepare an acetalization product having a degree of acetalization which assures the maintenance of good water solubility for a long time and is industrially stable.
As is apparent from the foregoing description, a detergent dispenser which comprises a powder detergent and a pouch or bag containing the powder detergent wherein the pouch is made of a cold water-soluble PVA derivative is heretofore unknown. The cold water-soluble PVA derivative is rapidly soluble in cold water, has excellent stability over time, does not undergo any change in crystallinity and has excellent acid resistance and alkali resistance.